It would be great to add diagrams to the guide. There have been a few discussions on zulip and some work by @chrissimpkins and @LeSeulArtichaut

• graphviz: https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide/topic/Proposal.3A.20New.20Rustc.20Guide.20Diagrams/near/189448735
  • https://hackmd.io/24S8FCKTS2mp8zVOdrDjww
• mermaid: https://rust-lang.zulipchat.com/#narrow/stream/196385-t-compiler.2Fwg-rustc-dev-guide/topic/mermaid.20support